docs: def robo_avatar_url(user_data, size=80):
      """Return the gravatar image for the given email address."""
      hash = md5(str(user_data).strip().lower().encode('utf-8')).hexdigest()
      url = "https://robohash.org/{hash}.png?size={size}x{size}".format(
          hash=hash, size=size)
      return url